【作者】 贺靖峰；

【导师】 赵跃民；

【作者基本信息】 中国矿业大学 ， 矿物加工工程， 2012， 博士

【摘要】 空气重介质流化床分选技术是一种适用于煤炭干法分选的高效分离工艺，为全球干旱缺水地区选煤技术的发展和应用提供了一条全新的路径和模式。在空气重介质分选基础理论的研究中发现，分选所采用的浓相气固流化床是一种非常复杂的气固多相流体系，因此有必要分别从宏观和微观层面对流化床内的多相流体动力学行为进行深入研究。本文基于“欧拉-欧拉”多相流模型，应用理论分析、试验测量与数值模拟计算相结合的方法，对流化床中的入料颗粒受力特性、气泡运动规律、加重质颗粒动力学行为及气固多相耦合作用机理等开展研究工作，以期为深入理解入料颗粒在流化床中的按密度分离规律、加重质密相与入料颗粒相的协同作用机理、完善流态化分选理论与研制和改进流化床分选设备等提供一定的理论支持。提出了采用“欧拉-欧拉”多相流模型对流化床内气固多相的复杂动力学行为进行数值计算研究。在总结大量经验模型和理论推导的基础上，针对本研究采用的浓相气固分选流化床，分别提出了气固曳力系数、颗粒间作用系数和固相应力项三种本构方程的理论计算公式来实现控制方程的封闭，为后续的数值模拟研究奠定了坚实基础。采用试验测量、数值模拟和理论模型验证相结合的方法，研究了流化床内的气泡动力学行为。结果表明，在表观流化气速1.5Umf≤U≤2.2Umf的条件下，气泡沿床层高度方向和床体轴向的平均直径分布分别为35mm<Db<49mm与40mm<Db<61mm。实验表明采用Rowe（1976）模型可对生成的气泡平均直径进行准确预测，由此推导出流化床内单个气泡上升速度的计算模型，为研究气泡动力学行为对入料颗粒在流化床中的运动规律及流化床分选效果的影响提供了理论依据。入料颗粒在流化床中的受力特性是粒群实现按流化床分选密度有效分离的基础。在对流化床中球形颗粒运动受力分析的基础上，建立了入料颗粒在流化床中运动时的受力平衡方程和基本动力学公式。自行设计了入料颗粒在流化床中运动时的受力测量系统，对不同粒径的球形颗粒在不同种类加重质形成的流化床中的受力进行测量。结果表明，入料颗粒的受力特性遵循稳定的变化规律，提出了受力均值和标准差随气速的变化关系均可由标准函数或修正后的标准函数表征。深入分析了颗粒连续受力的显著类周期性规律，获得了入料颗粒受力频率与振幅的波动范围。对入料颗粒在流化床中的受力波动数据进行分段拟合，建立了入料颗粒在流化床中瞬时受力的动力学拟合方程组。在试验测量、数值模拟和理论分析计算的基础上，对不同入料颗粒在流化床中的受力结果进行比较验证，结果表明，采用三种方法得到的颗粒瞬时受力均值与波动规律等基本保持一致。入料颗粒在流化床中的受力研究结果为探索不同密度的分选颗粒在流化床中的复杂动力学行为提供了必要条件。应用ICEM CFD软件构建与试验装置一致的三维流化床模型并进行精确网格划分，基于本文建立的适用于空气重介质流化床的数值计算模型，分别通过试验测量和数值模拟方法，对床层压降与密度分布进行定性与定量考察。结果证明流化床压降与标准差随气速的变化规律与加重质种类无关，只与U/Umf的数值有关。流化床密度分布规律的结果表明，1.5Umf≤U≤2.2Umf是床层密度分布最均匀稳定、波动幅度最小的操作气速范围，此时流化床的时均横向和轴向密度基本分布在1.95~2.10g/cm~3的范围内，密度标准差小于0.20g/cm~3，研究结果对完善流化床的压降和密度调控机制具有很好的促进作用。基于流化床压降和密度分布规律的试验和模拟结果，对流化床内的气固多相流体动力学行为进行深入的数值模拟研究。结果显示，流化稳定后，气相和加重质颗粒密相均处于均匀稳定分布状态，宏观上表现为床层活性较好，压降稳定，流化床三维空间内各点的密度分布很均匀，波动很小。微观上表现为气相具有很好的贯通性，颗粒相基本呈现稳定的环流和升降运动轨迹与速度变化规律，为入料粒群的分离提供了均匀稳定的分选密度环境，研究结果对流化床布风装置的设计和加重质的选取具有一定的参考价值和意义。本文在建立空气重介质流化床数值计算模型与自行研制的气泡运动采集系统和颗粒受力测量装置的基础上，通过对流化床中气泡动力学行为、入料颗粒受力特性、床层压降波动和密度分布特征、气相分布状态与加重质密相颗粒的运动规律、介质细颗粒与分选粗颗粒间的协同作用机理等开展深入研究，旨在为丰富流态化分选基本理论与流化床分选设备的研发改进及调控机制等发挥有效作用。该论文有图133幅，表29个，参考文献199篇。更多还原

【Abstract】 Air Dense Medium Fluidized Bed (ADMFB) is a highly effective separation technique fordry coal separation, which provides a novel method and pattern for the development andapplication of the coal classification technique in arid and hydropenic regions of the world. It isfound that the dense gas-solid fluidized bed is a complicated gas-solid multiphase fluid systemin the research process of the air dense medium separation theory. Therefore, it is significantlynecessary to conduct the further research on the multiphase fluid dynamical behavior of thefluidized bed from the macroscopical and microcosmic view respectively. Based on theEuler-Euler multiphase fluid model, the combination methods of theoretical analysis,experimental measurement and numerical simulation were applied to carry out the studying offorce measurement of the separation particles, moving bubbles behavior, dynamical behaviorsof the medium solids and coupling interaction mechanism between gas and solid phases. It aimsto provide the theoretical foundation for the classification mechanism of the separation particlesby the density, synergistic mechanism of interaction between the medium solids and separationparticles to complete the fluidization classification theory, and to develop and improve thefluidized separator.The Euler-Euler multiphase fluid model was proposed to conduct the numerical simulationon the complex gas-solid multiphase dynamical behaviors in the fluidized bed. On the basis of alarge quantity of empirical models and theoretical inferences, the constitutive equations of thegas-solid drag coefficient, particle-particle interaction coefficient and solid stress were raisedrespectively to approach the governing equations, which laid the solid foundation for thefollowing numerical simulation.The methods of experimental measurement, numerical simulation and theoretical modelverifying were combined to investigate the bubble dynamical behaviors in the fluidized bed.The results show that the mean diameter of35mm<Db<49mm along the direction of bed heightsand the mean diameter of40mm<Db<61mm along the axial direction were obtained with thesuperficial gas velocity of1.5Umf≤U≤2.2Umf. The Rowe (1976) model was raised to predict themean diameter of the generated bubbles. Then the rising velocity calculation model of thesingle bubble was also proposed. The models provide the theoretical foundation for the researchon the movement rules of the separation particles in the fluidized bed and separation efficiencycaused by the bubble dynamical behaviors.The force property of the separation particle in the fluidized bed is the basis to achieve theefficient separation of the feeding materials by the classification density of the fluidized bed.Based on the analysis of the force on the spheroidal particle moving in the fluidized bed, the load balance equation and basic dynamical formula of the separation particle in the Air DenseMedium Fluidized Bed were established finally. The force measurement device of theseparation particle was self-designed. The experimental measurements of the forces on twospheroidal particles with different particle sizes were conducted in the fluidized beds withdifferent types of medium solids respectively. The results indicate that the forces on theseparation particles moving in the fluidized bed follow the steady variation rules. The variationrelationship between the mean values and standard deviations of the forces and gas velocitycould be represented by the certain standard functions or corrected functions. The remarkablequasi-periodicity laws of the successive forces on the separation particles were further analyzed.The fluctuant ranges of the force frequency and amplitude of the separation particle areobtained finally.The force fluctuation data of the separation particle in the fluidized bed was carried out thepiecewise fitting. The dynamical fitting equations of the instantaneous forces were established.On the basis of experimental measurement, numerical simulation and theoretical calculation,the force results of different separation particles were detailedly compared. The results showthat the mean values and fluctuations of the forces on the separation particle are nearly closewith the application with above three approaches. The achievements provide the necessaryprerequisite for seeking for the complex dynamic behavior of the separation particles withdifferent densities in the fluidized bed.The3D model of the fluidized bed in accordance with the experimental device wasestablished with the software of ICEM CFD and the meshes were divided accurately. Based onthe numerical calculation model established in the study, the joint methods of experimentalmeasurement and numerical simulation were adopted to carry out the qualitative andquantitative investigation on the bed pressure drop and density distribution. The results showthe variation law of the bed pressure drop and its standard deviation with the gas velocity hasno relationship with the variety of medium solids, which only depends on the value of U/Umf.The study results of the bed density distribution show that1.5Umf≤U≤2.2Umfis the optimaloperation range, which could provide the steady and uniform bed density distributionenvironment. At this moment, the time-average bed densities of different bed heights anddifferent axial directions mainly distribute the range of1.95~2.10g/cm~3, and the standarddeviation of bed density is less than0.20g/cm~3. The achievements have great promotion tocomplete the regulation mechanism of the pressure drops and bed density.Based on the experimental and simulation results of the pressure drop and bed density of thefluidized bed, the further numerical simulation of the gas-solid multiphase fluid dynamicalbehaviors in the fluidized bed was carried out. The gas phase and the dense phase of medium solids both keep uniform and steady distribution condition after the stable fluidization. From themacroscopical view, it appears the favorable bed activity, stable sectional pressure drops anduniform bed density distribution of the fluidized bed. From the microcosmic view, it appears thefavorable connectivity of the gas phase in the fluidized bed, and the solid phase mainly presentsthe steady circumfluence, and elevation and subsidence movement trace and velocity variationrules. It not only ensures the steady flow of the fluidized bed, but also provides the stable anduniform bed density environment for the classification of the separation particles. The studyingresults have certain reference and significance on the distributor design of the fluidized bed andthe selection of medium solids.Based on the numerical calculation model and the self-designed acquisition system of thebubble movements and force measurement device of the separation particle, the bubbledynamical behavior, the force property of the separation particle, the fluctuation of pressuredrop and bed density distribution, gas phase distribution and movement laws of medium solids,synergistic mechanism of interaction between the medium solids and separation particles werefurther studied in the research. It aims to play the important effort on the basic separationtheories of the fluidization and the improvement and regulation mechanism of the fluidizedclassification equipments.更多还原